Portion of a mask



FIG. 1 is a front perspective view of a portion of a mask according to our design;

FIG. 2 is a rear perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a left side view thereof, with the right side view being a mirror image thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

Where included, broken lines showing environment or structure are for illustrative purposes only and form no part of the claimed design. 

The ornamental appearance for a portion of a mask, as shown and described. 